Incubation Period

incubation period [‚iŋ·kyə′bā·shən ‚pir·ē·əd]

(medicine)

The period of time required for the development of symptoms of a disease after infection, or of altered reactivity after exposure to an allergen.

(vertebrate zoology)

The brooding period required to bring an egg to hatching.

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Incubation Period 

(or incubation), the time interval from the moment of infection to the appearance of the clinical symptoms of a disease.

For each infectious disease, the incubation period has a characteristic length, although the length may vary depending on the number of microbes that entered the body, their pathogenicity, the physical condition of the body itself (previous traumas and illnesses, malnutrition, vitamin deficiency), and the site of entry of the infection. Vaccination, seroprophylaxis, and chemotherapy prolong the incubation period.

Table 1. Length of incubation periods of some infectious diseases
	Length of incubation period (in days)
	Most frequent “average”	Minimum	Maximum
Rabies . . . . . . .	40	12	3-6 months (rarely up to 1 year)
Botulism . . . . . .	12-24 hours	1-2 hours	1 (rarely more)
Brucellosis . . . . .	14	7	20-30
Typhoid fever . . .	14	3–4	21
Chicken pox . . . .	11–14	10	21
Influenza . . . . . .	2	a few hours	3
Dysentery . . . . .	3	2 hours	7
Diphtheria . . . . .	5	2	7–10
Whooping cough .	7–9	2	14–15
Measles . . . . . .	8–10	7	17 and 21 (with injection of serum)
Malaria . . . . . . .	10–15	6	31 (in tertian malaria, sometimes 7–11 months)
Epidemic parotitis (mumps) . . . . . .	11	9	21
Poliomyelitis . . . . .	7–14	3	35
Scarlet fever . . .	3–6	a few hours	7–12
Tetanus . . . . . . .	7–14	1	40 (sometimes upon removal of splinters, a few years)
Typhus . . . . . . .	12–14	6	20
Tularemia . . . . . . .	8	1	21
Epidemic cerebrospinal meningitis	2–3	a few hours	7
Foot-and-mouth disease . . . . .	4	2	6

In some infectious diseases (such as measles and diphtheria) causative agents are discharged into the environment during the incubation period; this leads to the infection of other persons. The length of the incubation period is important in discovering the source of infection and sometimes also for establishing a diagnosis.

IA. O. OL’SHANSKIT